1. Field of the Invention
Embodiments of the present disclosure relate to video processing, and more specifically, to predictive reference data transfer scheme for motion estimation.
2. Description of the Related Art
In high definition (HD) resolution encoding, large search range is usually employed for guaranteeing good video quality at limited bitrates. Some encoders use two approaches for fetching reference data from external memory to internal memory namely, growing window and sliding window. In both these approaches, large horizontal search ranges can be supported but only limited vertical search ranges are possible. Hence we will focus mainly on vertical search ranges. With the growing window approach, maximum vertical search range may be constrained by the availability of internal memory. Whereas, in the sliding window approach, usually; it is bandwidth of external memory to internal memory data transfer that can be supported. While horizontal search range in sliding window is constrained by the availability of internal memory. In some processors, growing window approach can support maximum vertical search range of +/−32 pixels, in case of predictive (P) picture, and +/−16 pixels, in case of bi-direction predictive (B) picture. Where as sliding window can support vertical search range of +/−64 pixels, in case of P picture, and +/−24 pixels, in case of B picture, for 256 KB of internal memory and with 1 GBPS external memory bandwidth for 1080 encoding. For IBBP encoding type, vertical search increase beyond +/−64 pixels for P picture and +/−24 pixels for B picture, which shows improvement in both PSNR as well as visual quality.
Other processors maintain a usage of +/−64 pixels vertical search range in case of B pictures; hence, large search ranges are essential for guaranteeing high quality video. However, this comes at the cost of significant increase in external memory bandwidth. For an example, increasing vertical search ranges to +/−96 pixels for P picture and +/−48 pixels for B picture increases external memory bandwidth by around 370 MBPS which will be restrictive on many devices.
Therefore, there is a need for reducing external memory bandwidth and still support larger search ranges.